The present invention relates generally to construction machinery, particularly to an excavator, and more particularly to a rod device for use as an arm of the excavator.
A known kind of excavator is a power shovel, which generally has a base structure generally formed as a caterpillar tractor, a boom pivotally supported at its lower end by the base structure, a means for changing inclination of the boom relative to the base structure, an arm pivotally supported near its root end by the upper end of the boom, an actuator mounted between an intermediate portion of the boom and the root end of the arm for changing inclination of the arm relative to the boom, and an excavating head such as a hoe mounted at the tip end of the arm. A power shovel of this kind can excavate only relatively shallow holes in the ground. In order to excavate relatively deep holes in the ground, it is known to remodel an excavator of the abovementioned structure so as to remove the hoe from the tip end of the arm, and instead to mount a clamshell bucket as suspended from the tip end of the arm by way of a cable adapted to be paid out from or wound up to the tip end of the arm. In this case, theoretically, a hole of any large depth can be excavated, by increasing the length of the cable. However, in the actual operation, as the cable becomes longer, the suspension of the clamshell bucket becomes more unstable, so as to cause larger swaying of the clamshell bucket, thereby requiring greater effort and longer time for the operator to place the clamshell bucket correctly at the position were excavation is to be done or at the position where the excavated material is to be dumped.